feature: add process swap column for Linux

[abuhurayraniloy]

Description

Adds the initial cross-platform support for an optional Swap column in the process widget.

On Linux, Bottom reads each process's swap usage from the VmSwap field in /proc/<PID>/status. The other platform collectors currently return no swap value, so the widget displays N/A on those platforms. The Swap column can be sorted like the other process columns.

This also updates the nightly schema, process-widget documentation, configuration documentation, and embedded/default configuration comments.

No dependencies were added or changed.

Issue

This PR addresses the Linux-first implementation discussed in #2001. It does not fully close the issue because native per-process swap collection for the other supported platforms remains future work.

Related to: #2001

Testing

Ran:

• ./scripts/schema/nightly.sh
• cargo fmt --check
• cargo clippy --all -- -D warnings
• cargo test

Manual testing:

• Ran Bottom on <Linux distribution/version>.
• Enabled the Swap column in the process configuration.
• Confirmed that Linux displays per-process swap usage.
• Confirmed that the column can be sorted.
• Confirmed that platforms without a swap value display N/A where tested.

Platforms tested:

• Windows
• macOS (specify version below)
• _Linux
  Ubuntu 26.04 LTS
• Other (specify below)

Checklist

• If this pull request adds or changes a dependency, please justify this in the description
• If this is a code change, areas your change affects have been linted using (cargo fmt)
• If this is a code change, your changes pass cargo clippy --all -- -D warnings
• If this is a code change, new tests were added if relevant
• If this is a code change, your changes pass cargo test
• The change has been verified to work (see the Testing section) and doesn't unexpectedly break anything else
• Documentation has been updated if needed (README.md, help menu, docs, configs, etc.)
• There are no merge conflicts
• You have personally reviewed your changes already before creating the PR
• The pull request passes the provided CI pipeline
• If the changes were generated with AI tools, ensure it follows the AI policy. Specify how it was used in the "Other" section, and that you as a human have personally reviewed the change

Other

AI assistance was used to help understand the existing Bottom codebase and draft documentation/configuration text. I personally reviewed the final changes and am responsible for the implementation and testing.

[ClementTsang]

Thanks for the PR! I'll take a look in the next few days.

[codecov]

Codecov Report

❌ Patch coverage is 81.95489% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.05%. Comparing base (8ddd0aa) to head (41b8018).

Files with missing lines	Patch %	Lines
src/widgets/process_table/process_data.rs	71.42%	10 Missing ⚠️
src/widgets/process_table.rs	66.66%	7 Missing ⚠️
src/collection/processes/linux/process.rs	89.36%	5 Missing ⚠️
src/collection/processes/linux/mod.rs	90.90%	1 Missing ⚠️
src/widgets/process_table/process_columns.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2224      +/-   ##
==========================================
- Coverage   63.63%   63.05%   -0.58%     
==========================================
  Files         136      136              
  Lines       19859    19986     +127     
==========================================
- Hits        12637    12602      -35     
- Misses       7222     7384     +162     

Flag	Coverage Δ
macos-14	52.03% <68.49%> (+0.31%)	⬆️
ubuntu-24.04	62.10% <81.53%> (-0.61%)	⬇️
windows-2022	51.75% <68.49%> (+0.31%)	⬆️

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[ClementTsang]

Some tentative comments, as well as noting this isn't supported for querying at the moment.

[abuhurayraniloy]

@ClementTsang, Let me know what you think of the updates.

[ClementTsang]

yep, will take a look!

[ClementTsang]

Apologies for the delay, will try to get to in the next few days.

[ClementTsang]

Will take a look in a bit, thanks!

[ClementTsang]

Found two more things while looking around and verifying things, otherwise seems fine.

[ClementTsang]

Cool, I think this looks fine. Thanks for your patience and sorry it took so long to review!

I'll merge once CI goes through.

---

Notes to things to follow up on after:

• Searching
• Swap%?
• Support on macOS/Windows/other platforms
• Cleaning up some of the code around process code

[ClementTsang]

@all-contributors please add @abuhurayraniloy for code

[allcontributors]

@ClementTsang

I've put up a pull request to add @abuhurayraniloy! 🎉

[abuhurayraniloy]

Thank you @ClementTsang!